This invention relates to a method for determining the relative wettability of a sample of a porous media with respect to two different liquids.
Wettability of a solid substance with respect to a particular liquid is a measure of the interaction of the liquid with the surfaces of the substance. In other words, wettability is a measure of the strength of adhesion of a liquid to surfaces with which it is in contact.
The relative wettability of a solid substance with respect to a first liquid and a second liquid refers to the comparison of the substance's wettability with respect to the first and second liquids. The relative wettability of a subterranean formation, made up of a porous media such as rock, with respect to oil and water is an important property in determining the suitability of the formation for secondary recovery of oil by waterflooding. Generally, waterflooding of a formation will be desirable only if that formation is water wettable; that is, is more wettable with respect to water than oil.
Heretofore, the primary method used to determine relative wettability of a sample of a porous media (i.e. core plug) with respect to oil and water is the relative displacement method of Ammott, described in Trans. AIME, vol. 216, pp. 156-162 (1959). This method generally involves displacement of oil and water from a core plug, and comprises a series of labor intensive steps which include centrifuging of the core plug to drive liquid therefrom. Liquid, therefore, must flow through and from the core plug. Consequently, accuracy of the method depends not only on interaction of surfaces of the core plug with either the oil or water, but also on the pore and pore throat (passages between pores) sizes and geometry. Moreover, it is difficult to apply the Ammott method to core plugs which are fractured or fragile.